Liquid crystal display devices are known for digital display in electronic calculators, clocks, household appliances, audio equipment, etc. Liquid crystal displays are being developed to replace cathode ray tube technology for display terminals. Liquid crystal displays occupy a smaller volume than cathode ray tube devices with the same screen area. Also, they are lighter than cathode ray tubes, and are therefore useful in portable device displays such as lap-top computers. In addition, liquid crystal display devices usually have lower power and lower voltage requirements than corresponding cathode ray tube devices.
One commercially available type of color filter array element that has been used in liquid crystal display devices for color display capability is a transparent support having a gelatin layer thereon which contains dyes having the additive primary colors red, green and blue in a mosaic pattern obtained by a photolithographic technique. To prepare such a color filter array element a gelatin layer is sensitized, exposed to a mask for one of the colors of the mosaic pattern, developed to harden the gelatin in the exposed areas, and washed to remove the unexposed (uncrosslinked) gelatin, thus producing a pattern of gelatin which is then dyed with dye of the desired color. The element is then recoated and the above steps are repeated to obtain the other two colors. Misalignment or improper deposition of color materials may occur during any of these operations. Further details of this process are disclosed in U.S. Pat. No. 4,081,277.
Color liquid crystal display devices generally include two spaced glass panels which define a sealed cavity that is filled with a liquid crystal material. For actively-driven devices, a transparent electrode is formed on one of the glass panels, which electrode may be patterned or not, while individually addressable electrodes are formed on the other of the glass panels. Each of the individual electrodes has a surface area corresponding to the area of one picture element, or pixel. If the device is to have color capability, each pixel must be aligned with a color area, e.g. red, green, or blue, of a color filter array. Depending on the image to be displayed, one or more of the pixel electrodes is energized during display operation to permit full light, no light, or partial light to be transmitted through the color filter area associated with that pixel. The image perceived by a user is a blending of colors formed by the transmission of light through adjacent color filter areas.
In the display of high quality images, the quality of the color filter array is quite important. Unfortunately, the cost of such color filter arrays is quite high and is one of the most costly components of the liquid crystal display. One promising method to reduce the cost of color filter array manufacture while still maintaining the required quality is by use of thermal dye transfer method as discussed in U.S. Pat. Nos. 4,923,860 and 5,229,232.
A difficulty with prior art apparatus is that they require the use of masks and also use contact printing. Masks are, of course, expensive and need to be moved in and out of position and contact printing has problems associated with wear and the difficulty to maintain in clean condition because contact printing necessarily produce particles through micro motion.